Silicon-on-plastic semiconductor device with interfacial adhesion layer

ABSTRACT

A semiconductor device and methods for manufacturing the same are disclosed. The semiconductor device includes a polymer substrate and an interfacial layer over the polymer substrate. A buried oxide layer resides over the interfacial layer, and a device layer with at least a portion of a radio frequency power switch that has a root mean square breakdown voltage in a range from 80 V to 200 V resides over the buried oxide layer. The polymer substrate is molded over the interfacial adhesion layer and has a thermal conductivity greater than 2 watts per meter Kelvin (W/mK) and an electrical resistivity greater than 10 12  Ohm-cm. Methods of manufacture for the semiconductor device include removing a wafer handle to expose a first surface of the buried oxide layer, disposing the interfacial adhesion layer onto the first surface of the buried oxide layer, and molding the polymer substrate onto the interfacial adhesion layer.

RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 14/715,830, filed May 19, 2015, entitled “METHOD OF MANUFACTUREFOR A SILICON-ON-PLASTIC SEMICONDUCTOR DEVICE WITH INTERFACIAL ADHESIONLAYER.”

U.S. patent application Ser. No. 14/715,830 claims priority to U.S.provisional patent application No. 62/000,264, filed May 19, 2014.

U.S. patent application Ser. No. 14/715,830 claims priority to and is acontinuation-in-part of U.S. patent application Ser. No. 14/260,909,filed Apr. 24, 2014, entitled “SILICON-ON-DUAL PLASTIC (SODP) TECHNOLOGYAND METHODS OF MANUFACTURING THE SAME,” which claims priority to U.S.provisional patent applications No. 61/815,327, filed Apr. 24, 2013, andNo. 61/816,207, filed Apr. 26, 2013. U.S. patent application Ser. No.14/260,909, is a continuation-in-part of U.S. patent application Ser.No. 13/852,648, filed Mar. 28, 2013, entitled “SEMICONDUCTOR DEVICE WITHA POLYMER SUBSTRATE AND METHODS OF MANUFACTURING THE SAME,” which claimspriority to U.S. provisional patent application No. 61/773,490, filedMar. 6, 2013.

U.S. patent application Ser. No. 14/715,830 claims priority to and is acontinuation-in-part of U.S. patent application Ser. No. 14/261,029,filed Apr. 24, 2014, entitled “PATTERNED SILICON-ON-PLASTIC (SOP)TECHNOLOGY AND METHODS OF MANUFACTURING THE SAME,” which claims priorityto U.S. provisional patent application No. 61/815,327, filed Apr. 24,2013, and No. 61/816,207, filed Apr. 26, 2013. U.S. patent applicationSer. No. 14/261,029, is a continuation-in-part of U.S. patentapplication Ser. No. 13/852,648, filed Mar. 28, 2013, entitled“SEMICONDUCTOR DEVICE WITH A POLYMER SUBSTRATE AND METHODS OFMANUFACTURING THE SAME,” which claims priority to U.S. provisionalpatent application No. 61/773,490, filed Mar. 6, 2013.

U.S. patent application Ser. No. 14/715,830 claims priority to and is acontinuation-in-part of U.S. patent application Ser. No. 14/529,870,filed Oct. 31, 2014, entitled “SILICON-ON-PLASTIC SEMICONDUCTOR DEVICEAND METHOD OF MAKING THE SAME,” which claims priority to U.S.provisional patent application No. 61/898,009, filed Oct. 31, 2013.

U.S. patent application Ser. No. 14/715,830 further relates to U.S.patent application Ser. No. 14/315,765, filed Jun. 26, 2014, entitled“SEMICONDUCTOR DEVICE WITH A POLYMER SUBSTRATE AND METHODS OFMANUFACTURING THE SAME.” U.S. patent application Ser. No. 14/315,765 isa continuation of U.S. patent application Ser. No. 13/852,648, filedMar. 28, 2013, which claims benefit of U.S. provisional patentapplication No. 61/773,490, filed Mar. 6, 2013.

All of the applications listed above are hereby incorporated herein byreference in their entireties.

FIELD OF THE DISCLOSURE

This disclosure relates to semiconductor devices and methods formanufacturing the same.

BACKGROUND

Radio frequency complementary metal oxide semiconductor (RFCMOS)silicon-on-insulator (SOI) RF power switches are devices that areessential for practically every mobile handset currently on the market.Existing RFCMOS SOI technologies used to manufacture these devicesprovide excellent performance in increasingly complex multi-throw RFswitches, tunable RF capacitance arrays, and antenna RF tuners.Conventional RFCMOS SOI technologies are built on high-resistivity CMOSwafer handles that have resistivities ranging from 1000 Ohm-cm to 5000Ohm-cm. A power switch employing RFCMOS SOI technology uses ahigh-resistivity wafer handle so that a plurality of relativelylow-voltage field-effect transistors (FETs) can be stacked whilemaintaining a desired isolation between the low-voltage FETs.

In an RF switch application for third generation (3G) and fourthgeneration (4G) wireless applications, a high degree of RF devicelinearity and a relatively very low level of RF intermodulation under RFpower conditions are crucial. Therefore, inherent nonlinearities in RFdevices such as CMOS n-type field-effect transistor (NFET) devices mustbe mitigated. Another source of nonlinearities is attributed to ahigh-resistivity silicon handle wafer region interfaced with a buriedoxide (BOX) dielectric region. One proposed solution for mitigatingthese nonlinearities includes a trap-rich silicon/oxide interface thatdegrades carrier lifetimes in the silicon/oxide interface. Otherproposed solutions for mitigating the nonlinearities due to thehigh-resistivity handle region interfaced with the BOX dielectric regioninclude harmonic suppression process techniques that include a series ofprocess steps and heating treatments to minimize nonlinearitiesattributed to the high-resistivity handle region interfaced with the BOXdielectric region. However, all the aforementioned proposed solutionsadd significant complexity and cost to CMOS SOI technology. What isneeded are CMOS SOI-based semiconductor devices and methods formanufacturing CMOS SOI devices that do not produce the nonlinearitiesattributed to the high-resistivity silicon handle region interfaced withthe BOX dielectric region.

SUMMARY

A semiconductor device and methods for manufacturing the same aredisclosed. The semiconductor device includes a polymer substrate and aninterfacial layer over the polymer substrate. A buried oxide layerresides over the interfacial layer, and a device layer with at least aportion of a radio frequency power switch that has a root mean square(RMS) breakdown voltage in a range from 80 V and 200 V resides over theburied oxide layer. The polymer substrate is molded over a interfacialadhesion layer and has a thermal conductivity greater than 2 watts permeter Kelvin (W/mK) and an electrical resistivity greater than 10¹²Ohm-cm. Methods of manufacture for the semiconductor device includesremoving a wafer handle to expose a first surface of the buried oxidelayer, disposing the interfacial adhesion layer onto the first surfaceof the buried oxide layer, and molding the polymer substrate onto theinterfacial adhesion layer.

In an exemplary embodiment, a second interfacial adhesion layer is overthe device layer, and a second polymer substrate is molded over thesecond interfacial adhesion layer. The second polymer substrate does notrequire identical characteristics to the polymer substrate molded to theinterfacial adhesion layer disposed on the first surface of the buriedoxide layer. However, the second polymer layer does have a thermalconductivity greater than 2 W/mK and an electrical resistivity greaterthan 10¹² Ohm-cm. Further still, additional method steps to fabricatethis exemplary embodiment include disposing the second interfacialadhesion layer over the device layer, and then molding the secondpolymer substrate directly onto the second interfacial adhesion layer.In at least one embodiment, an interlayer dielectric resides between thedevice layer and the second interfacial adhesion layer. Moreover, in atleast one embodiment, the second interfacial adhesion layer is disposeddirectly onto the interlayer dielectric.

Those skilled in the art will appreciate the scope of the disclosure andrealize additional aspects thereof after reading the following detaileddescription in association with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings incorporated in and forming a part of thisspecification illustrate several aspects of the disclosure and, togetherwith the description, serve to explain the principles of the disclosure.

FIG. 1 is a cross-sectional diagram of a semiconductor stack structureinterfaced with a relatively low-resistivity silicon wafer handle.

FIG. 2 is a cross-sectional diagram of the semiconductor stack structurewith a first polymer disposed on a first surface of the semiconductorstack structure.

FIG. 3 is a cross-sectional diagram of the semiconductor stack structureafter the relatively low-resistivity silicon wafer handle has beenremoved.

FIG. 4 is a cross-sectional diagram of the semiconductor stack structureafter a second polymer has been disposed on a buried oxide (BOX) layerto realize the semiconductor device of the present disclosure.

FIG. 5 is a cross-sectional diagram of the semiconductor stack structureafter a portion of the first polymer has been removed to expose theelectrical contacts to realize a completed semiconductor device.

FIG. 6 is a cross-sectional diagram of the semiconductor device showingheat flow paths through the semiconductor device with the polymer afterthe semiconductor device has reached a steady state powered condition.

FIG. 7 is a process diagram that yields the semiconductor device of FIG.6.

FIG. 8 is a specification table that lists thermal, mechanical,electrical, and physical specifications for an exemplary polymermaterial that is usable to form the polymer of the semiconductor deviceof the present disclosure.

FIG. 9 is a cross-sectional diagram of the semiconductor stack structureafter a first silicon nitride layer that is a first interfacial adhesionlayer has been deposited on the first surface of the semiconductor stackstructure.

FIG. 10 is a cross-sectional diagram of the semiconductor stackstructure after the first polymer has been deposited on the firstsilicon nitride layer.

FIG. 11 is a cross-sectional diagram of the semiconductor stackstructure after the silicon wafer handle has been removed.

FIG. 12 is a cross-sectional diagram of the semiconductor stackstructure after a second silicon nitride layer that is a secondinterfacial adhesion layer has been deposited on a second surface of thesemiconductor stack structure.

FIG. 13 is a cross-sectional diagram of the semiconductor stackstructure after the second polymer has been deposited on the secondsilicon nitride layer.

FIG. 14 is a cross-sectional diagram of the semiconductor stackstructure after a portion of the first polymer has been removed toexpose the electrical contacts.

FIG. 15 is a process diagram that yields a semiconductor device of FIG.14.

DETAILED DESCRIPTION

The embodiments set forth below represent the necessary information toenable those skilled in the art to practice the disclosure andillustrate the best mode of practicing the disclosure. Upon reading thefollowing description in light of the accompanying drawings, thoseskilled in the art will understand the concepts of the disclosure andwill recognize applications of these concepts not particularly addressedherein. It should be understood that these concepts and applicationsfall within the scope of the disclosure and the accompanying claims.

It will be understood that when an element such as a layer, region, orsubstrate is referred to as being “over,” “on,” “disposed on,” “in,” orextending “onto” another element, it can be directly over, directly on,directly in, or extend directly onto the other element or interveningelements may also be present. In contrast, when an element is referredto as being “directly over,” “directly on,” “directly disposed on,”“directly in,” or extending “directly onto” another element, there areno intervening elements present. It will also be understood that when anelement is referred to as being “connected” or “coupled” to anotherelement, it can be directly connected or coupled to the other element orintervening elements may be present. In contrast, when an element isreferred to as being “directly connected” or “directly coupled” toanother element, there are no intervening elements present.

Relative terms such as “below” or “above” or “upper” or “lower” or“horizontal” or “vertical” may be used herein to describe a relationshipof one element, layer, or region to another element, layer, or region asillustrated in the Figures. It will be understood that these terms andthose discussed above are intended to encompass different orientationsof the device in addition to the orientation depicted in the Figures.Moreover, the phrase “electrically resistive” used herein means having aresistance greater than 10⁶ Ohm-cm. Also, the phrase “thermallyconductive” used herein means having a thermal conductivity greater than2 watts per meter Kelvin (W/mK).

Traditional radio frequency complementary metal oxide (RFCMOS)silicon-on-insulator (SOI) technologies have reached a fundamentalbarrier due to limitations inherent to silicon wafer handles thatprevent the relatively better insulating characteristics available ingroup IV, group III-V, or sapphire wafer handles. The disclosedsemiconductor device replaces the silicon wafer handle with a polymer.As such, the semiconductor device of this disclosure eliminates the needfor a high-resistivity silicon wafer handle in a provided semiconductorstack structure.

Advanced silicon wafer handles for RF switch applications haveresistivities that range from 1000 Ohm-cm to 5000 Ohm-cm and aresignificantly more costly than standard silicon wafer handles havingmuch lower resistivities. Moreover, relatively complex process controlsare needed to realize high resistivity in advanced silicon waferhandles. For these reasons, standard silicon wafer handles are usedubiquitously in standard SOI technologies. However, standard siliconwafer handles with their much lower resistivities are not conducive forstacking a plurality of relatively low-voltage field-effect transistors(FETs) while maintaining a desired isolation between the low-voltageFETs. Fortunately, the polymer of the present disclosure replaces thesilicon wafer handle and thus eliminates the problems associated withboth high- and low-resistivity silicon wafer handles.

Additionally, the methods of the present disclosure allow for animmediate migration to 300 mm wafer handles for use in RF power switchapplications. This is an important development since there is currentlyno commercially viable high-volume supply of high-resistivity radiofrequency silicon-on-insulator (RFSOI) wafer handles in the 300 mm waferdiameter format. Fabricating the present semiconductor devices on 300 mmdiameter wafers would provide a significant improvement in die costs.Moreover, the need for a trap-rich layer and/or harmonic suppressiontechniques is eliminated, thereby resulting in a significantly simplerprocess flow and lower cost.

Further still, the polymer is expected to eliminate RF nonlinear effectsresulting from the interface between a buried oxide (BOX) layer and thesilicon wafer handle used in traditional semiconductor processes tomanufacture RF switch devices. The present methods realize RF switchdevices that have linear characteristics relatively close to ideallinear characteristics.

In this regard, RF linearity in a switch device is characterized byharmonics levels and intermodulation distortion for both an on state andan off state. In order to measure harmonics levels, a single RF tone ata given power level and frequency is fed into an input of the switch anda spectrum analyzer is used to measure power levels at twice an inputsignal frequency, which is the second harmonic, and three times thesignal frequency, which is the third harmonic. In particular, for outputpower levels of 25 dBm, harmonic levels less than about 110 dBm would beconsidered nearly ideal.

To measure intermodulation distortion, two closely spaced RF signals ata first frequency f1 and a second frequency f2 are fed into the switchinput so that adjacent harmonic power at 2*f2−f1 can be measured. Next,an intercept point known as the third order intercept point (IP3) isextrapolated to where this distortion power equals the power of the twoclosely spaced RF signals. Switches that are nearly ideal would have IP3levels that are greater than 90 dBm.

Additionally, the semiconductor device of this disclosure offers a nearideal voltage stacking of n-type field-effect transistors (NFETs).Traditionally, the number of NFET devices that can be stacked is limitedby silicon wafer handle resistivity combined with the interface effectsbetween the BOX layer and the silicon wafer handle. This issueessentially limits the number of practical NFETs that can be stacked andthus limits the highest RF operating voltage for the resulting NFETstack. Replacing silicon wafer handles with the polymer of the presentdisclosure allows relatively many more NFETs to be practically ideallystacked. The resulting semiconductor device is operable at relativelymuch higher RF power levels and root mean square (RMS) voltages than istraditionally allowable on silicon handle wafer technologies. It isexpected that a practically nearly ideal dielectric substrate such asthe one provided by this disclosure is able to withstand RMS voltagesgreater than at least 200 V, whereas typical silicon substrates cannotwithstand RMS voltages any greater than about 100 V.

In this regard, in the off state, the RF power switch must remain offduring relatively high RMS voltage levels that will exist across theterminals of the switch. In RFSOI type switches, preventing the switchfrom coming out of the off state is accomplished by stacking a largenumber of off-state metal oxide semiconductor (MOS) transistors inseries. In an ideal arrangement, an RF voltage across the switchterminals is equally distributed across an N number of MOS transistorsmaking up the RF switch. For example, an N=10 stack of MOS transistorswould ideally have 4 V across each MOS transistor for a total voltage of40 V across the entire N=10 stack of MOS transistors. In this idealcase, the 4 V across each MOS transistor would be just below thebreakdown voltage of each transistor. However, for a relatively large Nstack of MOS transistors, there is a departure from an ideal V/Nrelationship. For example, to withstand 80 V RMS an ideal stack of N=20transistors would be needed. However, in reality it has been discoveredthat N needs to be at least 30 transistors to withstand 80 V RMS. As aresult, for the purpose of the disclosure practically nearly idealstacking of transistors is defined as an upward deviation of no morethan 10% from the ideal linear relationship of V/N.

Furthermore, the highest RF frequency of operation of RF power switchesbuilt with the disclosed polymer can be extended beyond the highestfrequency of operation achievable with traditional RFCMOS SOItechnologies. Typically, a silicon wafer handle resistivity is in therange of 1000-3000 Ohm-cm, which effectively imposes an operationalhigh-frequency limit. The resulting resistivity of the polymer region inthe semiconductor device taught in this disclosure is several orders ofmagnitude higher than what is achieved in high-resistivity silicon. Forinstance, there are polymers with nearly ideal electrical insulatingcharacteristics, with resistivity values similar to what is obtained ingallium arsenide (GaAs) and sapphire semi-insulating wafer handles.

FIG. 1 is a cross-sectional diagram of a semiconductor stack structure10 interfaced with a relatively low-resistivity silicon wafer handle 12.In the exemplary case of FIG. 1, the semiconductor stack structure 10includes a buried oxide (BOX) layer 14, a field oxide layer 16, and adevice layer containing at least a portion of an NFET 18, with a gate20. A source metal conductor 22 couples a source contact 24 with asource flipchip bump 26. Similarly, a drain metal conductor 28 couples adrain contact 30 with a drain flipchip bump 32. An interlayer dielectric(ILD) 34 protects the gate 20 and supports the source flipchip bump 26and the drain flipchip bump 32.

FIG. 2 is a cross-sectional diagram of the semiconductor stack structure10 after a first polymer 36 having a relatively high thermalconductivity and relatively high electrical resistivity is disposed on afirst surface 37 of the semiconductor stack structure 10 that includesthe source flipchip bump 26 and the drain flipchip bump 32. The firstpolymer 36 has a thickness that at least encapsulates the sourceflipchip bump 26 and the drain flipchip bump 32 to protect them fromdamage during subsequent processing steps.

FIG. 3 is a cross-sectional diagram of the semiconductor stack structure10 after the relatively low-resistivity silicon wafer handle 12 has beenremoved. Once the semiconductor stack structure 10 is protected by thefirst polymer 36, the silicon wafer handle 12 may be removed by a numberof different techniques. One technique uses a conventional grindoperation that removes a majority of the silicon wafer handle 12followed by a selective wet or dry etch step of the remaining siliconwafer handle 12, and selectively stopping at a second surface 38 of thesemiconductor stack structure 10. In this exemplary case, the secondsurface 38 is also the exposed surface of the BOX layer 14. However, itis to be understood that the exposed portion of the semiconductor stackstructure 10 can be slightly deeper than the original second surface 38depending on etch duration. Other techniques for removal of the siliconwafer handle 12 exist and are well documented in the literature. Some ofthese other techniques are based on dry or wet etch processes. Theprocess used to remove the silicon wafer handle 12 is not particularlyrelevant to the present disclosure. However, it is desirable for theremoval of the silicon wafer handle 12 to be accomplished withoutdamaging the BOX layer 14 and the remainder of the semiconductor stackstructure 10, as well as the source flipchip bump 26 and the drainflipchip bump 32.

FIG. 4 is a cross-sectional diagram of the semiconductor stack structure10 after a second polymer 40 has been disposed on the BOX layer 14. Thepolymer material making up the first polymer 36 and the second polymer40 has a unique set of characteristics in that the polymer material isboth a relatively excellent electrical insulator and a relativelyexcellent heat conductor. Typical polymer materials making up commonplastic parts are extremely poor conductors of heat. Poor heatconduction is a common characteristic of plastics normally used in anover-mold operation. However, there are engineered polymer materialsthat do provide relatively excellent heat conduction. Variousformulations for such polymers yield thermal conductivities that rangefrom greater than 2 W/mK to around 50 W/mK. In one embodiment, thethermal conductivity of the polymer ranges from around about 50 W/mK toaround about 500 W/mK. Future enhancements in polymer science mayprovide additional improvements in terms of thermal conductivity whilemaintaining nearly ideal electrical insulating characteristics in thepolymer. The structure of this disclosure benefits from the maximizationof the polymer thermal conductivity, and it should be understood that anupper bound of polymer thermal conductivity nears a theoretical thermalconductivity of carbon nanotubes and graphene, which is 6600 W/mK.

It is desirable that a polymer material usable for the first polymer 36and second polymer 40 be relatively strongly bondable to the secondsurface 38 (FIG. 3) of the semiconductor stack structure 10. Forexample, the polymer material needs a bonding strength that allows thesemiconductor stack structure 10 to remain permanently bonded afteradditional processing steps, as well as throughout the operationallifetime of a semiconductor device comprising the semiconductor stackstructure 10. Moreover, a desirable thickness for the first polymer 36and the second polymer 40 ranges from around about 100 μm to aroundabout 500 μm, but other desirable thicknesses for the first polymer 36and the second polymer 40 can be thinner or thicker depending on thecharacteristics of the polymer material used to make up the firstpolymer 36 and the second polymer 40.

The polymer material making up the first polymer 36 and the secondpolymer 40 should also be a good electrical insulator. In general, theelectrical resistivity of the first polymer 36 and the second polymer 40should be greater than 10⁶ Ohm-cm. In at least one embodiment, thepolymer has a relatively high electrical resistivity that ranges fromaround about 10¹² Ohm-cm to around about 10¹⁶ Ohm-cm. In combinationwith relatively high electrical resistivity, the thermal conductivity ofthe first polymer 36 and the second polymer 40 is on the order of thethermal conductivity of typical semiconductors, which is typicallygreater than 2 W/mK. In one embodiment, the thermal conductivity of thefirst polymer 36 and the second polymer 40 ranges from greater than 2W/mK to around about 10 W/mK. In yet another embodiment, the thermalconductivity of the first polymer 36 and the second polymer 40 rangesfrom around about 10 W/mK to around about 50 W/mK. As polymer scienceprovides materials with additional thermal conductivities, thesematerials can be utilized in the semiconductor device of thisdisclosure. The semiconductor device of this disclosure benefits fromthe maximization of the polymer thermal conductivity, and it should beunderstood that an upper bound of polymer thermal conductivity nears atheoretical thermal conductivity of carbon nanotubes and graphene, whichis 6600 W/mK.

FIG. 5 is a cross-sectional diagram of the semiconductor stack structure10 after a portion of the first polymer 36 has been removed to exposethe source flipchip bump 26 and the drain flipchip bump 32 to realize acompleted semiconductor device 42. An exemplary process for removing aportion of the first polymer 36 includes a sample grind operation toetch back the first polymer 36 to expose at least electricallyconductive contact patches of the source flipchip bump 26 and the drainflipchip bump 32. In one embodiment, the source flipchip bump 26 and thedrain flip chip bump 32 should protrude from the remaining portion ofthe first polymer 36.

FIG. 6 is a cross-sectional diagram of the semiconductor device showingheat flow paths through the semiconductor device 42 with the secondpolymer 40 after the semiconductor device 42 has reached a steady statepowered condition. Under normal operation, heat is generated by energylosses in the NFET 18. An origin for the heat generated is representedby a dashed oval in the NFET 18 adjacent to the BOX layer 14. The flowof heat is represented by dashed arrows. As usual for high-performanceRF applications, the semiconductor device 42 is flipchip mounted in itsfinal application. As such, the heat to be extracted is transferred bythermal conduction to the source flipchip bump 26 and the drain flipchipbump 32. Thermal analysis of typical SOI technologies indicates thatunless the silicon wafer handle 12 (FIG. 1) is replaced with a goodthermal conductive material, the NFET 18 quickly overheats under nominalconditions and essentially becomes very unreliable and likely fails.Under normal conditions and design rules, back-end-of-line metallizationlayers (not shown) provide too high a thermal resistance path to be usedeffectively as a means to dissipate the heat generated by the device.The second polymer 40 accomplishes effectively the same function as theoriginal silicon wafer handle 12 from a thermal management point of viewwhile also providing much improved linear characteristics andeffectively much higher electrical resistivity than the 1 kOhm-cmelectrical resistivity of the silicon wafer handle 12.

FIG. 7 is a process diagram that yields the semiconductor device 42having the second polymer 40 disposed on the second surface 38, which inthis exemplary case is an exposed portion of the semiconductor stackstructure 10. However, it is to be understood that the exposed portionof semiconductor stack structure 10 can be slightly deeper than theoriginal second surface 38 depending on etch duration. The exemplaryprocess begins with providing the semiconductor stack structure 10having the second surface 38 of the BOX layer 14 in direct contact withthe silicon wafer handle 12 (step 100). While the semiconductor stackstructure 10 is attached to the silicon wafer handle 12 at the beginningof the process, it is to be understood that a wafer handle made of othergroup IV or III-V semiconductors is also usable in place of the siliconwafer handle 12. The first polymer 36 having a high electricalresistivity and a high thermal conductivity is disposed to completelycover the contacts made up of the source flipchip bump 26 and the drainflipchip bump 32 (step 102). The process then continues by removing thesilicon wafer handle 12 to expose the second surface 38 of thesemiconductor stack structure 10 (step 104). The second polymer 40 canthen be disposed on the second surface 38 using various polymer materialdisposing methods (step 106). Such methods for attaching the secondpolymer 40 to the semiconductor stack structure 10 include, but are notlimited to, injection molding, spin deposition, spray deposition, andpattern dispensing of polymer material directly onto the second surface38 of the semiconductor stack structure 10. Once the second polymer 40is attached to the second surface 38 of the semiconductor stackstructure 10, the first polymer 36 is partially removed to expose thecontacts made up of the source flipchip bump 26 and the drain flipchipbump 32 (step 108).

The semiconductor device 42 can then be cleaned with common chemicalsolvents and/or plasma cleaning processes. The semiconductor device 42can then be singulated from an original wafer (not shown) intoindividual die by a number of different conventional processes.Typically, a saw operation that cuts through the semiconductor stackstructure 10 and first polymer 36 and the second polymer 40 is onemethod of die singulation. Other singulation methods such as lasersawing, laser scribing, or diamond scribing can be used as alternatives.

It should be noted that the semiconductor device and methods taught inthis disclosure begin with a conventionally manufactured RFSOI CMOSwafer, which in this exemplary case is the semiconductor stack structure10 disposed on the silicon wafer handle 12. However, one distinction isthat there is no need for the silicon wafer handle 12 to have highresistivity, since the silicon wafer handle 12 is removed and does notbecome part of the semiconductor device 42. If the semiconductor device42 requires flipchip packaging, it should ideally already include thesource flipchip bump 26 and the drain flipchip bump 32, although such arequirement may not be necessary depending on the specificcharacteristics of the bump or pillar packaging technology employed. Inthis exemplary case, it is assumed that a wafer process was completedthrough bumping.

FIG. 8 is a specification table that lists thermal, mechanical,electrical, and physical specifications for an exemplary polymermaterial that is usable to form the first polymer 36 and the secondpolymer 40 of the semiconductor device 42. The exemplary polymermaterial specified in the specification table of FIG. 8 is made by CoolPolymers® and is sold under the label “CoolPoly® D5506 ThermallyConductive Liquid Crystalline Polymer (LCP).” It is to be understoodthat the specification table of FIG. 8 only provides exemplaryspecifications and that a variety of mechanical and physical propertiesare available within the scope of the present disclosure. Moreover, thequantitative values for the thermal and electrical properties providedin the table of FIG. 8 only represent exemplary values that are withinthe range of thermal and electrical properties already discussed in theabove disclosure. The first polymer 36 and the second polymer 40 are athermoplastic such as polyamides that include nylon. Other suitablethermoplastics include, but are not limited to, acrylonitrile butadienestyrene (ABS), polyetheretherketone (PEEK), and polysulfone. In someembodiments, the first polymer 36 and the second polymer 40 can be athermoset plastic, such as a two-part epoxy resin. Moreover, the firstpolymer 36 and the second polymer 40 typically include an admixture forincreasing thermal conductivity. Examples of suitable thermalconductivity enhancing admixtures include ceramic powders, whichinclude, but are not limited to, boron nitride powder and aluminumnitride powder.

FIG. 9 is a cross-sectional diagram of the semiconductor stack structure10 after a first silicon nitride layer 44 that is a first interfacialadhesion layer has been deposited on the first surface 37 of thesemiconductor stack structure 10 that includes the source flipchip bump26 and the drain flipchip bump 32. The first silicon nitride layer 44 isan adhesion promoter for bonding a first polymer 36 to the semiconductorstack structure 10. However, it is to be understood, that other adhesionpromoters are available and are within the scope of the presentdisclosure. For example, one adhesion promoter that would also be usableis aluminum nitride (AlN).

FIG. 10 is a cross-sectional diagram of the semiconductor stackstructure 10 after a first polymer 36 has been deposited on the firstsilicon nitride layer 44. The first polymer 36 has a high electricalresistivity and a high thermal conductivity and completely covers theelectrical contacts made up of the source flipchip bump 26 and the drainflipchip bump 32. The electrical contacts are completely covered by thefirst polymer 36 to protect them during subsequent processing steps.

FIG. 11 is a cross-sectional diagram of the semiconductor stackstructure 10 after the relatively low-resistivity silicon wafer handle12 has been removed. Once the semiconductor stack structure 10 isprotected by the first polymer 36, the silicon wafer handle 12 may beremoved by a number of different techniques. One technique uses aconventional grind operation that removes a majority of the siliconwafer handle 12 followed by a selective wet or dry etch step of theremaining silicon wafer handle 12, and selectively stopping at a secondsurface 38 of the semiconductor stack structure 10. In this exemplarycase, the second surface 38 is also the exposed surface of the BOX layer14. However, it is to be understood that the exposed portion of thesemiconductor stack structure 10 can be slightly deeper than theoriginal second surface 38 depending on etch duration. Other techniquesfor removal of the silicon wafer handle 12 exist and are well documentedin the literature. Some of these other techniques are based on dry orwet etch processes. The process used to remove the silicon wafer handle12 is not particularly relevant to the present disclosure. However, itis desirable for the removal of the silicon wafer handle 12 to beaccomplished without damaging the BOX layer 14 and the remainder of thesemiconductor stack structure 10 as well as the source flipchip bump 26and the drain flipchip bump 32.

FIG. 12 is a cross-sectional diagram of the semiconductor stackstructure 10 after a second silicon nitride layer 46 that is a secondinterfacial adhesion layer has been deposited on the second surface 38(FIG. 11) of the semiconductor stack structure 10. In this exemplarycase, the second silicon nitride layer 46 is disposed directly onto theBOX layer 14. The second polymer 40 (not shown) can then be disposed onthe second silicon nitride layer 46 using various polymer materialdisposing methods. In this exemplary case, the second polymer 40 ismolded directly onto the second silicon nitride layer 46.

FIG. 13 is a cross-sectional diagram of the semiconductor stackstructure 10 after the second polymer 40 has been disposed on the secondsilicon nitride layer 46. In one respect, the first silicon nitridelayer 44 and the second silicon nitride layer 46 are adhesion promotersfor bonding the first polymer 36 and the second polymer 40 to thesemiconductor stack structure 10. In another respect, the first siliconnitride layer 44 and the second silicon nitride layer 46 prevent or atleast resist a diffusion of moisture within the first polymer 36 and thesecond polymer 40 from reaching the BOX layer 14 or other criticaldevice layers that may include CMOS layers. The benefit of having amoisture barrier formed by the first silicon nitride layer 44 and thesecond silicon nitride layer 46 is the prevention of a degradation offunction of devices that make up the semiconductor stack structure 10.The first silicon nitride layer 44 and the second silicon nitride layer46 may be deposited as an example via a plasma-enhanced chemical vapordeposition (PECVD) system by the decomposition of silane and nitrogengases, as commonly known to those skilled in the art. Such PECVD systemsoperate at temperatures typically between room temperature and 350° C.The first silicon nitride layer 44 and the second silicon nitride layer46 may also be deposited by other techniques, including liquid phasechemical vapor deposition (LPCVD) and sputtered from a nitride targetusing RF sputtering. The first silicon nitride layer 44 does notsignificantly impact the thermal conductivity provided by the firstpolymer 36. Likewise, the second silicon nitride layer 46 does notsignificantly impact the thermal conductivity provided by the secondpolymer 40. In one embodiment, the thickness of either of the firstsilicon nitride layer 44 and the second silicon nitride layer 46 rangesfrom around about 100 Å to around about 1000 Å. In another embodiment,the thickness of either of the first silicon nitride layer 44 and thesecond silicon nitride layer 46 ranges from around about 1000 Å toaround about 5000 Å. In yet another embodiment, the thickness of eitherof the first silicon nitride layer 44 and the second silicon nitridelayer 46 ranges from around about 5000 Å to around about 10,000 Å.

FIG. 14 is a cross-sectional diagram of the semiconductor stackstructure 10 after a portion of the first polymer 36 has been removed toexpose the source flipchip bump 26 and the drain flipchip bump 32 torealize a completed semiconductor device 48. An exemplary process forremoving a portion of the first polymer 36 includes a sample grindoperation to etch back the first polymer 36 to expose at leastelectrically conductive contact patches of the source flipchip bump 26and the drain flipchip bump 32. In one embodiment, the source flipchipbump 26 and the drain flip chip bump 32 should protrude from theremaining portion of the first polymer 36.

FIG. 15 is a process diagram that yields the semiconductor device havingthe first polymer 36 disposed on the first silicon nitride layer 44 andthe second polymer 40 disposed on the second silicon nitride layer 46.An exemplary process begins with providing the semiconductor stackstructure 10 having the first surface 37 including contacts such assource flipchip bump 26 and drain flipchip bump 32, along with thesecond surface 38 of the BOX layer 14, in direct contact with thesilicon wafer handle 12 (step 200). While the semiconductor stackstructure 10 is attached to the silicon wafer handle 12 at the beginningof the process, it is to be understood that a wafer handle made of othergroup IV or III-V semiconductors is also usable in place of the siliconwafer handle 12.

The first silicon nitride layer 44 is deposited on the first surface 37of the semiconductor stack structure 10 that includes the contacts madeup of the source flipchip bump 26 and the drain flipchip bump 32 (step202). The first polymer 36 having a high electrical resistivity and ahigh thermal conductivity is disposed on the first silicon nitride layer44 to completely cover the contacts made up of the source flipchip bump26 and the drain flipchip bump 32 (step 204). The process then continuesby removing the silicon wafer handle 12 to expose the second surface 38of the semiconductor stack structure 10 (step 206). Next, a secondsilicon nitride layer 46 is deposited on the second surface 38 of thesemiconductor stack structure 10 (step 208). The second polymer 40 canthen be disposed on the second silicon nitride layer 46 using variouspolymer material disposing methods (step 210). Such methods forattaching the second polymer 40 to the second silicon nitride layer 46of the semiconductor stack structure 10 include, but are not limited to,injection molding, spin deposition, spray deposition, and patterndispensing of polymer material directly onto the second silicon nitridelayer 46. Once the second polymer 40 is attached to the second siliconnitride layer 46, the first polymer 36 is partially removed to exposethe contacts made up of the source flipchip bump 26 and the drainflipchip bump 32 (step 212).

Those skilled in the art will recognize improvements and modificationsto the embodiments of the present disclosure. All such improvements andmodifications are considered within the scope of the concepts disclosedherein and the claims that follow.

What is claimed is:
 1. A semiconductor device comprising: a polymersubstrate; an interfacial adhesion layer over the polymer substrate; aburied oxide layer over the interfacial adhesion layer; and a devicelayer over the buried oxide layer and comprising at least a portion of aradio frequency power switch that has a root mean square (RMS) breakdownvoltage in a range from 80 V to 200 V, wherein the polymer substrate ismolded over the interfacial adhesion layer and has a thermalconductivity greater than 2 watts per meter Kelvin (W/mK) and anelectrical resistivity greater than 10³ Ohm-cm.
 2. The semiconductordevice of claim 1 wherein the polymer substrate is molded directly onthe interfacial adhesion layer.
 3. The semiconductor device of claim 1wherein the interfacial adhesion layer is disposed directly on theburied oxide layer.
 4. The semiconductor device of claim 1 wherein theburied oxide layer is disposed directly on the device layer.
 5. Thesemiconductor device of claim 1 wherein the interfacial adhesion layeris a silicon nitride layer.
 6. The semiconductor device of claim 1wherein the interfacial adhesion layer is between about 100 Angstromsand about 250 Angstroms.
 7. The semiconductor device of claim 1 whereinthe interfacial adhesion layer is between about 250 Angstroms and about500 Angstroms.
 8. The semiconductor device of claim 1 wherein theinterfacial adhesion layer is between about 500 Angstroms and 1000Angstroms.
 9. The semiconductor device of claim 1 wherein the thermalconductivity of the polymer substrate ranges from greater than 2 W/mK toaround about 10 W/mK.
 10. The semiconductor device of claim 1 whereinthe thermal conductivity of the polymer substrate ranges from aroundabout 10 W/mK to around about 50 W/mK.
 11. The semiconductor device ofclaim 1 wherein the thermal conductivity of the polymer substrate rangesfrom around about 50 W/mK to around about 6600 W/mK.
 12. Thesemiconductor device of claim 1 wherein the electrical resistivity ofthe polymer substrate ranges from around about 10¹² Ohm-cm to aroundabout 10¹⁶ Ohm-cm.
 13. The semiconductor device of claim 1 wherein theelectrical resistivity of the polymer substrate ranges from around about10³ Ohm-cm to around about 10¹² Ohm-cm.
 14. The semiconductor device ofclaim 1 wherein the polymer substrate has a thickness that ranges fromaround about 10 μm to around about 100 μm.
 15. The semiconductor deviceof claim 1 wherein the polymer substrate has a thickness that rangesfrom around about 100 μm to around about 500 μm.
 16. The semiconductordevice of claim 1 wherein the polymer substrate has a thickness thatranges from around about 500 μm to around about 1000 μm.
 17. Thesemiconductor device of claim 1 further including a second interfacialadhesion layer disposed over the device layer, and a second polymersubstrate molded directly onto the second interfacial adhesion layer.18. The semiconductor device of claim 1 wherein the radio frequencypower switch comprises at least one field-effect device.
 19. Thesemiconductor device of claim 1 wherein the polymer substrate is athermoplastic.
 20. The semiconductor device of claim 1 wherein thepolymer substrate is a thermoset plastic.